The present invention relates to the securing of door or hatch locks in aircrafts, which locks are to be manually operated, particularly unlocked for opening the respective door and hatch.
The doors of airplanes are usually unlocked in that a door opening lever is actuated for unlocking its locking mechanism. Whenever a door or a hatch is provided as an emergency exit, the locking mechanism is coupled to the lever actuating the door or hatch so that a single motion of that lever unlocks and opens the door.
Such a device is, for example, disclosed in U.S. Pat. No. 3,004,303. This patent discloses particularly projections or noses arranged along the frame periphery of the door as well as at the door itself and these noses face and engage each other when the door is locked. Upon raising the door the projections or noses of the door pass through the gaps and spaces between the projections on the frame.
In the closed position, the doors and hatches are maintained in position through friction between the respectively engaging noses particularly because the higher pressure inside of the aircraft cabin provides an outwardly directed force which acts accordingly on the door and reenforces the frictional engagement between the noses. In addition, bolts running in longitudinal direction of the aircraft secure the locking position of the door. For unlocking and opening, a particular lever is manually operated so that in fact a single motion of the lever unlocks and opens the door.
This mode of operation satisfies the international requirements for airplane safety. The reason is particularly to be seen in that the door may also serve as an emergency exit and must be opened rather quickly. As long as the pressure in the cabin is sufficiently larger than the outside pressure, it is not possible to open the door, simply because it is impossible to manually overcome the friction between the projections as reinforced by this pressure differential. However, if the aircraft is still very close to ground, either because it just took off or it is just about ready to approach the runway for landing, this differential is minimal or non-existent so that the friction will no longer impede the opening of the door, and, in fact, a single motion of that lever will permit opening of the door even if the craft is still in flight. It is, however, quite undesirable that in such case, while the plane has still or already considerable speed, it is actually possible to open the door.